Objectives of the project are as follows: first to identify sexual dimorphisms and the role of gonadal steroids in the regulation of neural and glial signal transduction, proliferation, and survival and in the ontogeny of brain neurotransmitter systems; second, to resolve the mechanisms of both the acute (e.g. enhanced apoptosis) and subacute (e.g. altered neurotransmitter receptor message) neural effects of gonadal steroids; third, to develop an animal model for behavioral effects of gonadal steroid withdrawal and for the differential behavioral effects of acute alterations in gonadal steroid levels. These objectives serve two overall goals: 1) Understanding neuroregulatory mechanisms of gonadal steroids of relevance for affective disorders; and 2) Defining the substrate of differential sensitivity, the process by which the same hormonal stimulus can elicit different responses in different subjects. Findings in the past year include the following: 1) Dramatic sex-related differences in the distribution of neurons exhibiting metabotropic and ionotropic responses to glutamate (97%/2.5% in females vs 29%/70% in males) 2) Sex-dependent differences in the effect of an estrogen receptor alpha agonist (PPT) on glutamate-induced calcium channel current (augmented in females, unaffected in males); 3) Significantly increased heat shock protein (HSP) and pAkt concentrations in male vs female rodent cortical neurons; 4) dissociation of the effects of estrogen receptor alpha and beta agonists on ERK, with ER alpha inhibiting and ER beta increasing ERK activation; 5) Behavioral despair (increased immobility in the forced swim test) in rats withdrawn from estradiol replacement. These data suggest that gender and gonadal steroids are significant regulators of interneuronal and intracellular signaling. Further, these data help identify new mechanisms underlying sex-dependent differences in neuronal development (through glutamatergic differentiation) and neuronal response (through HSP and calcium channel regulation). They also illustrate the extent to which variability in response to a hormone (estradiol) may be mediated through inter-individual or tissue-specific differences in the relative concentrations of ER alpha and beta. Finally, the estradiol withdrawal-induced behavioral effects shown in the forced swim test are very promising as a means for identifying the cellular concomitants and genomic predictors of gonadal steroid change-induced behavioral perturbation.